If you have a computer with an SSD drive, and a standard 1TB drive, and moved your Documents folder to D:/, and your addons are not showing up ingame, you have to move your Documents folder back to the C:/ drive.

Your addons should be here: C:/Users/Your name/Documents/Addons/and here 1 folder for each addon.

If you moved your Documents folder to D:/ to save space on your SSD, the game will not follow the Documents folder to D:/ and therefore will not load them.

I don't know if you can change the location to D:/Users/Your Name/Documents/Addons/addon folders, I'll try that, someday lol.